1. Technical Field of the Invention
The present invention relates to a compact and size-reduced key sheet used for various portable equipment with a terminal for a mobile communication system such as a portable telephone or a motor-vehicle telephone.
2. Related Art
In recent years, there has been a sheet-shaped key top made by combining a plastic film with a key top body made of thermoplastic resin in a push button used for the portable equipment.
As its manufacturing method, the method has been described in Japanese Laid-open Patent Publication No. SHO. 54-154461 and Japanese Patent Publication No. HEI. 7-54656, in which a resin film are molded integrally with the key top body by putting a resin film between the mold to injection-mold the thermoplastic resin.
As shown in FIG. 3, these are the manufacturing methods that a display section 8 and a colored layer 6 are applied by printing on a surface or a back face of a plane film 2 to put the resin film between a mold and then to inject the thermoplastic resin, thereby molding the key top body 1 and forming integrally the plane-shaped film 2 with the key top body 1.
At present, a color tone of the display section has come to be various kind of color tones as an achromatic color such as black and gray, chromatic color such as red, blue and green, and a metallic color such as gold or silver. The metallic color of all is obtained by mixing aluminum powder and mica powder or the like and pigment into paint and ink or the like.
Recently, a requirement for the display section with the sense of a mirror surface has been increased. However, it has been difficult to realize the display section and the layer with the sense of the mirror surface as obtained by manufacturing methods such as a plating process or hot stamping by application such as coating or printing on the surface.
As the general manufacturing method of the layer and the display section with the sense of the mirror surface, it has been known that on a surface of the key top body molded into a predetermined shape in advance is provided the layer and the display section with the sense of the mirror surface by the plating process or hot stamping. Since the layer and the display section are worn in practical uses, it becomes necessary to give wear-resistance resin coating on the surface of the display section, resulting in frequent occurrence of defects due to dust and foreign matters at mass production and an increase in cost of manufacturing due to an increase of the number of production processes.
On the other hand, although it has been studied that the layer or the display section with the sense of the mirror surface is provided by plating process or hot stamping on the back face of the plane film to draw the film into a predetermined shape and to mold integrally with the thermoplastic resin, the layer with the sense of the mirror surface can not follow elongation of the film on the occasion of drawing process of the film, so that a crack or the like is occurred, therefore, it also has been not preferable from the outside appearance.
Furthermore, it is also required to combine with a lightening function through the sense of the mirror surface and a backup light.
The invention, for solving the problems described above, is to realize a key sheet having the layer or a display section with the sense of the mirror surface by providing at a low cost an inorganic substance of a thin film which a crack is not occurred even though being drawn on the back of the film, and in addition, to provide the key sheet which also embodies the illuminating effects.
That is the invention provides a key sheet which a film is integrated on a surface and a side of a key top body made of thermoplastic resin, said key sheet comprising on the back face of the film an inorganic substance layer which is 20 to 100 nm in thickness and is 1 to 20% in a transmittance of visible light.
Furthermore, the invention provides a key sheet of a vacuum evaporation layer which is formed by a physical vapor deposition method or a chemical vapor deposition.
Furthermore, the invention provides a key sheet which the inorganic substance layer forms a hollow-character shaped display section.
Furthermore, the invention provides a key sheet which a display section is formed between the film and the inorganic substance layer.
The inorganic substance layer according to the invention is preferably 20 to 100 nm in thickness and 1 to 20% in a transmittance of visible light. When the thickness of the layer is less than 20 nm, the sense of the mirror surface can not be obtained due to the thinness.
Moreover, since a crack becomes tendency to occur on the occasion of drawing processing of the film, the illuminating effects can not be obtained when the thickness of the layer exceeds 100 nm. The more preferable range is 40 to 80 nm. Moreover, when the transmittance of visible light is less than 1%, the illuminating effects by the backup light can not be obtained. Moreover, when the transmittance of visible light exceeds 20%, the sense of the mirror surface becomes not able to obtain. The further preferable range is 2 to 15 nm. The transmittance of visible light of the invention conforms to the method of JIS K-7105.
The inorganic substance layer according to the invention is preferably the vacuum evaporation layer and is formed by the physical vapor deposition or the chemical vapor deposition. By either of the methods, an uniform film without inconsistencies can be formed, and an ion plating method, a sputtering method or the like is given in the physical vapor depositions, and a plasma CVD method, a photo assisted CVD method or the like is given in the chemical vapor depositions.
A thermoplastic resin according to the invention is preferable the thermoplastic resin with transparency, and a polyethylene resin, a polypropylene resin, a polystyrene resin, a polycarbonate resin, a polyacrylic resin, a polymethacrylic acid resin and a polyamide resin are given.
As the film according to the invention, all the films can be available as far as being the film excellent in transparency. In particular, a haze is preferably less than 10%. Moreover, a material is preferable a nonextensible polyamide film or an alloy film of a polycarbonate and a poly-butylene-terephthalate or the like is preferable, taking drawing property into account.
Furthermore, 50 to 200 nm is adaptable in the film thickness.
The material used for the inorganic substance layer according to the invention is preferably aluminum or chromium which the sense of the mirror surface is easy to be manifested at a low cost.
An ink used for the display section, a coloring layer, a protective layer, a holding layer or the like of the invention is selected and used properly from an urethane base ink, acrylic base ink, a vinyl base ink, a polycarbonate base ink and a polyester base ink or the like, taking an adhesion between each of layers into account.